Technical Field
The present invention relates to an image encoding device that encodes images.
Related Art
Encoding schemes, such as the Moving Picture Experts Group (MPEG) scheme, have developed as a technique for digitizing large volumes of moving image information and recording or transmitting it. The MPEG-1, MPEG-2, MPEG-4 and H.264/Advanced Video Coding (AVC) specifications, and the like have been employed as international standard encoding schemes. These schemes have been applied to digital satellite broadcast systems, Digital Versatile Discs (DVDs), portable phones, digital cameras, and the like. Currently, au utilization range of the schemes is increasingly expanding, and they have accordingly become familiar.
In the specifications above, an encoding target image (also referred to below as simply a “target image”), which is an image to be encoded, is predicted in blocks with image information (referred to below as a “decoded image” or “reference image”) that has undergone an encoding process. Subsequently, a difference (referred to below as “predicted difference” as appropriate) between the target image and the original image is encoded. In this way, these specifications reduce the amount of code data by eliminating redundancy of moving images. In particular, an inter prediction (also referred to as an inter-frame prediction or inter-screen prediction), which refers to a decoded image that differs from the target image, achieves a highly accurate prediction by designating a block (referred to below as a “reference block”) in the reference image (decoded image) which has a strong correlation with an encoding target block (referred to below as a “target block”) in the target image. In addition, a motion vector that represents a difference in coordinates between the target block and the reference block is also encoded, independently of the predicted difference.
In encoding a motion vector, a motion vector (referred to below as a “prediction vector”) for a target block is predicted from motion vectors for blocks positioned around the target block. Subsequently, a difference between the motion vector and the prediction vector is encoded as the motion vector (e.g., JP 2008-278091 A). In this case, the amount of generated code may be heavily dependent on the prediction vector. Therefore, when a motion search process for searching a reference image for a block that has a strong correlation with a target block and a mode selecting process for determining an optimum prediction method (intra or inter prediction) are performed, the amount of generated code to be generated may be estimated by referring to the above difference. Furthermore, in order to increase the accuracy of the motion search, a search start point may be determined with the prediction vectors for the surrounding blocks.
On the other hand, currently, dedicated LSIs for image processing which conform to standard specifications such as the H.264/AVC are being developed (e.g., “Standard technology (layout of system LSI) database: image processing LSI/data compressing LSI,” [online], JPO, [Search date: Oct. 11, 2011], Internet <URL: http://www.jpo.go.jp/shiryou/toushin/chousa/0007.html>).